With recent advancement of digital technologies, electronic equipment such as portable information devices and home information appliances have been developed to provide higher functionality. For this reason, demands for an increase in a capacity of a nonvolatile memory element, reduction in a write electric power in the nonvolatile memory element, reduction in write/read time in the nonvolatile memory element, and longer life of the nonvolatile memory element are now increasing.
Under the circumstances in which there are such demands, it is said that there is a limitation on miniaturization of the existing flash memory using a floating gate. On the other hand, a nonvolatile memory element (resistance variable memory) using a resistance variable layer as a material of a memory section is formed by a memory element having a simple structure in which the resistance variable layer is sandwiched between a pair of electrodes. Therefore, further miniaturization, a higher-speed, and lower electric power consumption of the nonvolatile memory element are expected.
When using the resistance variable layer as the memory section, the resistance variable layer changes from a high-resistance state to a low-resistance state or from the low-resistance state to the high-resistance state, for example, by applying electric pulses. In this case, it is necessary to clearly distinguish between these two states, i.e., the high-resistance state and the low-resistance state, to enable changing between the low-resistance state and the high-resistance state stably at a high-speed, and to retain these two states in a nonvolatile manner. For the purpose of stabilization of such memory characteristics and miniaturization of memory elements, a variety of proposals have been proposed heretofore.
As one of such proposals, there is known a nonvolatile memory element using tantalum oxide as a resistance variable material forming a resistance variable layer (e.g., Patent Literature 1). This tantalum oxide is binary, and therefore its composition control and layer fabrication are relatively easy. Besides, it could be said that the tantalum oxide has a relatively high compatibility with semiconductor manufacturing process steps.